Hi All, Ive recently install a thermal store connected to a gas boiler and back boiler stove and im having a few teething problems which hopefully someone with more grey matter than me can assist with....

Its a 210L Advanced Appliances multi fuel thermal store, its connected to Ideal 40kW combi boiler which also still supplies some of the hot taps and a fairly old 14kW (5 to room, 9 to water) Hunter Herald stove. The TS runs my central heating (radiators and underfloor) and the remainder of the DHW (mainly the bath). I will use the immersion heaters too once solar is fitted.

All seems to be working generally as it should it terms of controls, when the stove is lit the pump runs and depending where the thermostats are set the boiler switches off.
However the TS is suppose to operate at 75-80 degrees according to the instructions, but im struggling to get it up to that temperature using the boiler or the stove, 60-65 is more realistic. The boiler is set on max temperature (80 degrees) but unless i run it flat out for hours on end the TS seems happier at around 65 degrees.

Im not sure if i was expecting too much from the back boiler stove but even after several hours with a good fire the output temperature is still only 60 degrees. The TS has a blending valve which controls the flow back to the stove which according to the instructions should be set at 55-60 degrees. It is a multifuel stove so maybe im not getting anywhere near the maximum output burning wood and would need to burn coal which im reluctant to do. Ive experiments with various pump speeds for the stove pump and also tried closing the valves to the heat leak radiators which is plumbed between the flow and return but im still not able to achieve more than 60 degrees.

Any help or advice would be much appreciated

Details of the Thermal Store:

https://www.youtube.com/watch?v=UX1O1kcvo1Q&t=13s

https://www.advanceappliances.co.uk/product/70-multi-fuel-universal-thermal-store-sfuts/

Thanks for your response
The boiler is 2yrs old, the thermal store is new, the stove was bought second hand and must be around 8-10years old
The install is a combination of professional and DIY!! I’ve done a lot of the work but with input from professionals.
Did you see the video for the TS showing how the blending valve works?
I’m trying to heat the store with no load.
I will get an IR thermometer as currently just working from the temp gauge on the store and some clip on pipe gauges. All pipe work associated with the stove doesn’t really get above 60-65 degrees when it’s been lit for several hours. I need to do some work insulating pipe work as I suspect I’m losing heat in the combi pipe work.
The back boiler has 4 tappings and I’ve currently got the flow into the bottom and return opposite top.

Posted By: Dan BarlowDid you see the video for the TS showing how the blending valve works?

Seen that now, My guess is that they put it there as the only way to guarantee one is fitted. IMO better placed at the stove but there's no choice now.

Posted By: Dan BarlowI will get an IR thermometer as currently just working from the temp gauge on the store and some clip on pipe gauges.

Clip ons work, I suggested an IR thermometer as it saves buying lots of clip ons. If you have the clip ons all around then no need for an IR thermometer. (although I find an IR thermometer useful for all sorts of things).

Posted By: Dan BarlowI need to do some work insulating pipe work as I suspect I’m losing heat in the combi pipe work.

uninsulated pipes loose 60W/m at 55 deg and 40W/m at 40 deg for a 22mm pipe, 28mm pipe figures are 80W/m and 50W/m. you can calculate the losses from your pipes.

Posted By: Dan BarlowThe back boiler has 4 tappings and I’ve currently got the flow into the bottom and return opposite top.

The way I am reading this its a bit confusing to me.
The flow to the TS should be at the top and the return from the TS to the bottom of the stove.

Posted By: Dan BarlowThe install is a combination of professional and DIY!! I’ve done a lot of the work but with input from professionals.

The problem with combined DIY and professional work is the apportionment of blame when things go wrong. Unless the professionals are good and have a care it is easy for them to walk away blaming the other guy (you) when things go wrong. - Have you asked them for their opinion as to why the TS fails to get up to temperature?

Posted By: WillInAberdeenthere's no need to store heat from a combi boiler;

Correct but I don't see a 250 ltr tank as a useful TS for heating (mine is 2000 lts) This one is more of a way of combining various heat sources to do one job prioritising cheap or renewable heat over fossil fuel heat.

Posted By: WillInAberdeen'Heat leak' safety radiator on log stove?

Yes - not really needed as as if things start to get over hot the assumption I would make is that the intelligent owner would stop piling on the logs.

When the combi is trying to heat the TS is is running all the time or is it cycling on and off?

The overheat thermostats could be stopping the supply of heat to the TS if they are faulty or wired incorrectly. To what temp. are they set.

Posted By: Dan BarlowI’d normally fill the stove with wood and then leave it for an hour or two. I suspect it’s not producing anywhere near the maximum output as I’m burning wood not coal.

Stove outputs quoted by manufactures are typically the best achievable to give their stoves consumer appeal. Which means that the rated output will be with good quality firewood at mid-burn. when just lit, after reloading or near the end of a load the output will be very much reduced.

Firewood is very variable in its heating capabilities but a reasonable calculation is about 3.5 kWh / kg. Even if you burn coal you will still be subject to low output on start up, at reloading and towards the end of the load.

Typical household coal is about 7 kWh / kg. which will give longer times between refuelling and more time at max output.

Don't expect to be able to run your stove at 9 kW to water for very long because at that rate you will be putting 5 kW to air and the room in which the stove sits will become unbearably hot after an hour or two. This is one of the problems with wood stoves that have back boilers.

Your combi should get the TS up to temp. fairly quickly. In your place I would be addressing the issue of the combi not heating the TS properly as a first step as it is easier to run without putting unwanted heat into the house. Once you have cracked this one then address the stove problem - you may find the same reasons apply.

With the combi running measure the pipe temps and note the burn cycling and pump run times. Most combi boilers have an integrated CH pump and I note that the TS also has a pump for the gas boiler circulation. Are you inadvertently using 2 pumps or is one out of the circuit.

IMO you should try to the resolve the issue now whilst the installation is new. It is much better to talk to the manufactures and professionals now rather than in the autumn when you have to start off by saying "Do you remember that system you installed months ago............."

Thanks again everyone for your input, much appreciated.
The boiler circuit is just using the boiler pump, the pump on the TS store has been removed.
It is a sealed system with expansion vessel (no F&E tank).
I will ensure that the heat leak radiator is not left isolated this was done to eliminate this from soaking up all of the stoves output.

I clearly need to do a little more investigating with pipe temperatures etc.
I take on board your comment about doing it now rather than in the autumn when nobody can remember the install and we are desperate for the heating!